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The battery-free phone developed at the UW can sense speech, actuate the earphones, and switch between uplink and downlink communications, all in real time. It is powered by either ambient radio signals or light.Mark Stone/University of Washington

Today’s phones pack millions of times more computing punch than all of the computers used to put man on the moon during the Apollo-era. You can certainly do a lot of things with a smartphone nowadays but all of those apps and constant WIFI ramblings between multiple connections take a drain on battery life. In this day and age, the recent developments reported by University of Washington researchers of a battery-free phone are even more remarkable than they sound at face-value. Effectively, this is a mobile, cordless smartphone that can even make a Skype call.

Forget about charging (but also Facebook)

“We’ve built what we believe is the first functioning cellphone that consumes almost zero power,” said co-author Shyam Gollakota, an associate professor in the Paul G. Allen School of Computer Science & Engineering at the UW. “To achieve the really, really low power consumption that you need to run a phone by harvesting energy from the environment, we had to fundamentally rethink how these devices are designed.”

This prototype only uses a few micro-watts of power to operate rather than the 100 micro-watts a typical cell phone requires to make a voice call. To draw power, the battery-free phone harvests energy from the ambient light using tiny photodiodes. Everything inside the phone is optimized to use as less power as possible. The system also draws power, albeit in minute amounts, from RF signals transmitted from a computer called the basestation located as far as 31 feet (9.4 m) away.

One major challenge the researchers had to overcome was to figure a way to run an operating system continuously. Other research groups that have dabbled with battery-free devices circumvented this issue by designing them with alternating periods of operation and power harvesting during which the device would be shut down. That would be impractical for a phone, though.

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“You can’t say hello and wait for a minute for the phone to go to sleep and harvest enough power to keep transmitting,” said co-author Bryce Kellogg, a UW electrical engineering doctoral student. “That’s been the biggest challenge — the amount of power you can actually gather from ambient radio or light is on the order of 1 or 10 microwatts. So real-time phone operations have been really hard to achieve without developing an entirely new approach to transmitting and receiving speech.”

Instead, the University of Washington researchers incorporated only analog components. This way, their device could make use of something called ‘analog backscatter’ which both receives and reflects signal, allowing the system as a whole to use less power.

Remarkably, the battery-free phone was used to make a live Skype call over a cellular network via the custom bridged basestation.

It’s not clear yet when a similar phone to this prototype will be available to consumers but the introduction of more efficient 5G networks could make it all possible.

Now, the team is focusing on extending the phone’s operating range but also on encrypting conversations to make them secure. Moreover, they’re also interested in running video streams on a low-power E-ink screen, as crazy as that may sound for a battery-less phone.